This invention relates in general to power line filtering techniques and more particularly to an active technique for providing bandpass filtering and transient suppression in power lines.
In the past, electromagnetic interference (EI) power line filters have used large capacitors and inductors in various series and parallel combinations to provide high-frequency filtering. For power lines carrying heavy currents (100 amps), the size of the inductors is limited by heating losses and the voltage drop across the inductors and the size of the capacitors is limited by the tolerable reactive current shunted to ground. In general, a compromise is made with the result that the filter is ineffective at low frequencies and becomes effective only for frequencies in excess of 1 KHz. When transient protection is desired, it must be provided by another device tacked onto the conventional EMI filter.